The present invention relates to adaptive data processing systems, and more particularly to adaptive preprocessing systems which extract information relating samples in order to modify incoming data which is intended to be further processed in radar Moving Target Indicators and similar systems.
Signal processing equipment in general is designed to receive only particular desired information for evaluation. However, as is often the case, the desired information is not isolated by itself, but is found in the presence of unwanted signals. Depending on the purpose of the system these unwanted signals may take the form of information that is either correlated or uncorrelated with prior information-data samples. In other words, it is often desirable to remove either components of the signal that appear the same (i.e., correlated) in each information-data sample or signal components that appear to change from one sample to the next (i.e., information uncorrelated between samples).
The importance of extracting information of this nature is clear and well-known in diverse applications of data processing. For example, a pattern recognition system is concerned primarily with information that is correlated from sample to sample. Similarly, in a Moving Target Indication radar system, "sea clutter" or "chaff" are represented by data which is relatively slowly changing (with respect to a moving target); thus the correlated information between successive radar samples is comprised predominately of interference or otherwise non-relevant information that should be eliminated.
Prior data processing systems of various types, as well as the present invention, have attempted to utilize either the correlated or uncorrelated components between successive data samples in modifying incoming data for further processing. But prior techniques generally employ either parallel canceller loops or series iterative loops which function in an equivalent manner. Parallel loop or equivalent techniques are unsatisfactory basically because they are interactive in nature, that is, the action of one loop depends upon the effects the actions of other loops. These interactive loops are unsatisfactory because they have longer setting times than independent canceller loops and must employ reduced loop gain to prevent loop-to-loop oscillation. In the series-iterative technique, undesirable aspects include the requirement for a large or excessive number of stages, thus increasing system size and cost, while at the same time reducing system reliability.
Copending Pat. Application Ser. No. 580,395 entitled "Adaptive MTI" by Frank F. Kretschmer, Jr., Bernard L. Lewis and James P. Hansen, filed in the United States on an even data herewith and assigned to the same assignee of the present invention discloses a system somewhat similar to the present invention, although it is of different type (in that it is of limited iterative nature) and is configured in a different manner.
Accordingly, the present invention has been developed to overcome specific shortcomings of the above know, and similar techniques, and to provide a data processing technique for minimizing or enhancing particular aspects of an incoming data sample through resort to extraction of independent information between successive samples.